Video coding method and device, and recording medium having bitstream stored therein

Abstract

An image decoding method and device according to the present disclosure may configure an intra-merge list for a current block, and generate a prediction block for the current block on the basis of at least one of a plurality of candidates belonging to the intra-merge list. Here, a candidate belonging to the intra-merge list may be derived on the basis of a reference block, and the reference block may belong to at least one of a current picture or a reference picture.

Description

Video coding method and device, and recording medium storing bitstream

[0001] The present invention relates to a video signal processing method and device.

[0002] The market demand for high-resolution video is growing, necessitating technologies capable of efficiently compressing high-resolution images. To address this market need, the ISO / IEC's Moving Picture Expert Group (MPEG) and the ITU-T's Video Coding Expert Group (VCEG) jointly formed the Joint Collaborative Team on Video Coding (JCT-VC). They completed development of the HEVC (High Efficiency Video Coding) video compression standard in January 2013 and have been actively conducting research and development on next-generation compression standards.

[0003] Video compression largely consists of intraprediction, interprediction, transform, quantization, entropy coding, and in-loop filtering. Among these, intraprediction refers to a technique that generates a prediction block for the current block using reconstructed pixels surrounding the current block. The encoder encodes the intraprediction mode used for intraprediction, and the decoder performs intraprediction by reconstructing the encoded intraprediction mode.

[0004] The present disclosure provides a method and device for deriving information regarding intra prediction of a current block.

[0005] The present disclosure provides a method and device for constructing an intra merge list for deriving information regarding intra prediction of a current block.

[0006] The present disclosure provides a method and device for generating a prediction block of a current block based on a plurality of candidates in an intra merge list.

[0007] The video decoding method and device according to the present disclosure can construct an intra merge list for a current block and generate a prediction block for the current block based on at least one of a plurality of candidates belonging to the intra merge list. Here, the candidate belonging to the intra merge list can be derived based on a reference block, and the reference block can belong to at least one of the current picture and the reference picture.

[0008] In the image decoding method and device according to the present disclosure, the candidate may include at least one of a directional or non-directional intra prediction mode of the reference block.

[0009] In the video decoding method and device according to the present disclosure, when the reference block uses a method for deriving an intra prediction mode, the candidate may include information on whether the decoder side uses a method for deriving an intra prediction mode and an intra prediction mode already derived from the reference block.

[0010] In the image decoding method and device according to the present disclosure, when the reference block has a block vector, the candidate may include information about an intra prediction method used by the reference block and the block vector of the reference block.

[0011] In the video decoding method and device according to the present disclosure, when the reference block generates a final prediction block based on a weighted sum of prediction blocks generated in an intra prediction mode or prediction blocks generated with a block vector, the candidate may include information regarding weights applied to the prediction blocks used in the weighted sum.

[0012] In the video decoding method and device according to the present disclosure, when the reference block generates a prediction block based on a block vector, the candidate may include information regarding the difference between the template region of the position referenced by the block vector of the reference block and the template region of the current block.

[0013] In the video decoding method and device according to the present disclosure, when the reference block uses a prediction method (e.g., DIMD, etc.) that implicitly derives an intra prediction mode based on a gradient filter, the candidate may include at least one of information about an amplitude value derived through the gradient filter or a weight derived through the amplitude value. Here, the gradient filter may mean a filter that derives a gradient based on a difference in luma component values.

[0014] In the video decoding method and device according to the present disclosure, when the reference block uses a prediction method (e.g., TIMD, etc.) that implicitly derives an intra prediction mode based on a template cost, the candidate may include at least one of information about the template cost or a weight derived through the template cost. Here, the template cost may mean at least one of a difference in a template area between the reference block and a block referenced by the reference block, or between the reference block and the current block, or between the block referenced by the reference block and the current block.

[0015] In the video decoding method and device according to the present disclosure, the candidate may include information about the reference block. Here, the information about the reference block may include at least one of the size of the reference block, the transformation method used for restoration, the filter parameters within the loop, or a heterogeneous list that can be used in intra prediction or a heterogeneous list that can be used in inter prediction.

[0016] In the video decoding method and device according to the present disclosure, a plurality of intra merge lists separated by the intra prediction mode determination method can be generated based on the intra prediction mode determination method of the reference block.

[0017] In the video decoding method and device according to the present disclosure, the prediction block of the current block can be generated based on a weighted sum between prediction blocks generated based on candidates corresponding to the top K list indices in the intra merge list. Here, K can be a natural number.

[0018] The video encoding method and device according to the present disclosure can construct an intra merge list for a current block and generate a prediction block for the current block based on at least one of a plurality of candidates belonging to the intra merge list. Here, the candidate belonging to the intra merge list can be derived based on a reference block, and the reference block can belong to at least one of the current picture and the reference picture.

[0019] The bitstream transmission method and device according to the present disclosure can transmit a bitstream generated by the image encoding method.

[0020] A computer-readable recording medium according to the present disclosure can store a bitstream encoded by the image encoding method.

[0021] According to the present disclosure, by generating a prediction block through an intra merge list for the current block, more accurate prediction is possible, thereby improving the compression performance of the encoder / decoder.

[0022] According to the present disclosure, by weighting prediction blocks generated based on candidates in an intra merge list, more accurate prediction is possible, thereby improving the compression performance of a decoder / encoder.

[0023] According to the present disclosure, by constructing a plurality of intra merge lists according to an intra prediction method of a reference block, efficient prediction becomes possible, and thus the compression performance of a decoder / encoder can be improved.

[0024] According to the present disclosure, by transmitting a candidate index including information for generating a prediction block of a current block, the overall bit rate is reduced, thereby improving the compression performance of a decoder / encoder.

[0025] FIG. 1 is a block diagram showing an image encoding device according to the present disclosure.

[0026] FIG. 2 is a block diagram showing an image decoding device according to the present disclosure.

[0027] FIG. 3 illustrates an intra prediction method according to the present disclosure.

[0028] The video decoding method and device according to the present disclosure can construct an intra merge list for a current block and generate a prediction block for the current block based on at least one of a plurality of candidates belonging to the intra merge list. Here, the candidate belonging to the intra merge list can be derived based on a reference block, and the reference block can belong to at least one of the current picture and the reference picture.

[0029] In the image decoding method and device according to the present disclosure, the candidate may include at least one of a directional or non-directional intra prediction mode of the reference block.

[0030] In the video decoding method and device according to the present disclosure, when the reference block uses a method for deriving an intra prediction mode, the candidate may include information on whether the decoder side uses a method for deriving an intra prediction mode and an intra prediction mode already derived from the reference block.

[0031] In the image decoding method and device according to the present disclosure, when the reference block has a block vector, the candidate may include information about an intra prediction method used by the reference block and the block vector of the reference block.

[0032] In the video decoding method and device according to the present disclosure, when the reference block generates a final prediction block based on a weighted sum of prediction blocks generated in an intra prediction mode or prediction blocks generated with a block vector, the candidate may include information regarding weights applied to the prediction blocks used in the weighted sum.

[0033] In the video decoding method and device according to the present disclosure, when the reference block generates a prediction block based on a block vector, the candidate may include information regarding the difference between the template region of the position referenced by the block vector of the reference block and the template region of the current block.

[0034] In the video decoding method and device according to the present disclosure, when the reference block uses a prediction method (e.g., DIMD, etc.) that implicitly derives an intra prediction mode based on a gradient filter, the candidate may include at least one of information about an amplitude value derived through the gradient filter or a weight derived through the amplitude value. Here, the gradient filter may mean a filter that derives a gradient based on a difference in luma component values.

[0035] In the video decoding method and device according to the present disclosure, when the reference block uses a prediction method (e.g., TIMD, etc.) that implicitly derives an intra prediction mode based on a template cost, the candidate may include at least one of information about the template cost or a weight derived through the template cost. Here, the template cost may mean at least one of a difference in a template area between the reference block and a block referenced by the reference block, or between the reference block and the current block, or between the block referenced by the reference block and the current block.

[0036] In the video decoding method and device according to the present disclosure, the candidate may include information about the reference block. Here, the information about the reference block may include at least one of the size of the reference block, the transformation method used for restoration, the filter parameters within the loop, or a heterogeneous list that can be used in intra prediction or a heterogeneous list that can be used in inter prediction.

[0037] In the video decoding method and device according to the present disclosure, a plurality of intra merge lists separated by the intra prediction mode determination method can be generated based on the intra prediction mode determination method of the reference block.

[0038] In the video decoding method and device according to the present disclosure, the prediction block of the current block can be generated based on a weighted sum between prediction blocks generated based on candidates corresponding to the top K list indices in the intra merge list. Here, K can be a natural number.

[0039] The video encoding method and device according to the present disclosure can construct an intra merge list for a current block and generate a prediction block for the current block based on at least one of a plurality of candidates belonging to the intra merge list. Here, the candidate belonging to the intra merge list can be derived based on a reference block, and the reference block can belong to at least one of the current picture and the reference picture.

[0040] The bitstream transmission method and device according to the present disclosure can transmit a bitstream generated by the image encoding method.

[0041] A computer-readable recording medium according to the present disclosure can store a bitstream encoded by the image encoding method.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings attached to this specification so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts irrelevant to the description have been omitted to clearly explain the present invention, and similar parts have been designated with similar reference numerals throughout the specification.

[0043] Throughout this specification, when a part is said to be 'connected' to another part, this includes not only cases where they are directly connected, but also cases where they are electrically connected with another element in between.

[0044] Additionally, whenever a part throughout this specification is said to "include" a component, this does not mean that other components are excluded, but rather that other components may be included, unless specifically stated otherwise.

[0045] Additionally, while terms such as "first," "second," etc. may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another.

[0046] Additionally, in the embodiments of the devices and methods described herein, some components of the devices or some steps of the methods may be omitted. Furthermore, the order of some components of the devices or some steps of the methods may be changed. Furthermore, other components or other steps may be inserted into some components of the devices or some steps of the methods.

[0047] Additionally, some components or some steps of the first embodiment of the present invention may be added to the second embodiment of the present invention, or some components or some steps of the second embodiment may be replaced.

[0048] In addition, the components shown in the embodiments of the present invention are independently depicted to represent different characteristic functions, and this does not mean that each component is composed of separate hardware or a single software component. That is, each component is described by listing each component for convenience of explanation, and at least two components among each component may be combined to form a single component, or a single component may be divided into multiple components to perform a function. Such integrated and separate embodiments of each component are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

[0049] In this specification, a block can be variously expressed as a unit, an area, a unit, a partition, etc., and a sample can be variously expressed as a pixel, a pel, a pixel, etc.

[0050] Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings. In describing the present invention, duplicate descriptions of identical components will be omitted.

[0051] FIG. 1 is a block diagram showing an image encoding device according to the present disclosure.

[0052] Referring to FIG. 1, a video encoding device (100) may include a picture segmentation unit (110), a prediction unit (120, 125), a transformation unit (130), a quantization unit (135), a reordering unit (160), an entropy encoding unit (165), an inverse quantization unit (140), an inverse transformation unit (145), a filter unit (150), and a memory (155).

[0053] The picture segmentation unit (110) can segment the input picture into at least one processing unit. At this time, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). Hereinafter, in the embodiments of the present disclosure, the coding unit may be used to mean a unit that performs encoding or a unit that performs decoding.

[0054] A prediction unit may be divided into at least one square or rectangular shape of the same size within a single coding unit, or may be divided such that one prediction unit among the divided prediction units within a single coding unit has a different shape and / or size from another prediction unit. When a prediction unit that performs intra prediction based on a coding unit is generated and is not the minimum coding unit, intra prediction can be performed without being divided into a plurality of NxN prediction units.

[0055] The prediction unit (120, 125) may include an inter prediction unit (120) that performs inter prediction or inter prediction, and an intra prediction unit (125) that performs intra prediction or intra prediction. It may determine whether to use inter prediction or intra prediction for a prediction unit, and determine specific information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. A residual value (residual block) between the generated prediction block and the original block may be input to the transformation unit (130). In addition, prediction mode information, motion vector information, etc. used for prediction may be encoded together with the residual value by the entropy encoding unit (165) and transmitted to the decoder.

[0056] The inter prediction unit (120) may predict a prediction unit based on information of at least one picture among the previous or subsequent pictures of the current picture, and in some cases, may predict a prediction unit based on information of a portion of an encoded region within the current picture. The inter prediction unit (120) may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

[0057] The reference picture interpolation unit can receive reference picture information from the memory (155) and generate pixel information less than an integer pixel from the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter with different filter coefficients can be used to generate pixel information less than an integer pixel in units of 1 / 4 pixels. In the case of a chrominance signal, a DCT-based 4-tap interpolation filter with different filter coefficients can be used to generate pixel information less than an integer pixel in units of 1 / 8 pixels.

[0058] The motion prediction unit can perform motion prediction based on a reference picture interpolated by the reference picture interpolation unit. Various methods such as FBMA (Full search-based Block Matching Algorithm), TSS (Three Step Search), and NTS (New Three-Step Search Algorithm) can be used to derive a motion vector. The motion vector can have a motion vector value in units of 1 / 2 or 1 / 4 pixels based on the interpolated pixel. The motion prediction unit can predict the current prediction unit by using different motion prediction methods. Various methods such as Skip Mode, Merge Mode, AMVP Mode, Intra Block Copy Mode, and Affine Mode can be used as motion prediction methods.

[0059] The intra prediction unit (125) can generate a prediction unit based on reference pixel information surrounding the current block, which is pixel information within the current picture. If the surrounding block of the current prediction unit is a block on which inter prediction has been performed and the reference pixel is a pixel on which inter prediction has been performed, the reference pixel included in the block on which inter prediction has been performed can be replaced and used with reference pixel information of the surrounding block on which intra prediction has been performed. That is, if the reference pixel is not available, the unavailable reference pixel information can be replaced and used with at least one reference pixel among the available reference pixels.

[0060] Additionally, a residual block containing residual value information, which is the difference between the prediction unit that performed the prediction based on the prediction unit generated in the prediction unit (120, 125) and the original block of the prediction unit, can be generated. The generated residual block can be input to the transformation unit (130).

[0061] In the transformation unit (130), the residual block including the residual value information of the prediction unit generated through the original block and the prediction unit (120, 125) can be transformed using a transformation method such as DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), or KLT. Whether to apply DCT, DST, or KLT to transform the residual block can be determined based on the intra prediction mode information of the prediction unit used to generate the residual block.

[0062] The quantization unit (135) can quantize values ​​converted to the frequency domain by the transformation unit (130). The quantization coefficients may vary depending on the block or the importance of the image. The values ​​produced by the quantization unit (135) can be provided to the dequantization unit (140) and the reordering unit (160).

[0063] The rearrangement unit (160) can perform rearrangement of coefficient values ​​for quantized residual values.

[0064] The rearrangement unit (160) can change a two-dimensional block-shaped coefficient into a one-dimensional vector form through a coefficient scanning method. For example, the rearrangement unit (160) can change the two-dimensional block-shaped coefficient into a one-dimensional vector form by scanning from the DC coefficient to the coefficient of the high-frequency region using a zig-zag scan method. Depending on the size of the transformation unit and the intra prediction mode, a vertical scan that scans the two-dimensional block-shaped coefficient in the column direction or a horizontal scan that scans the two-dimensional block-shaped coefficient in the row direction may be used instead of the zig-zag scan. That is, depending on the size of the transformation unit and the intra prediction mode, it is possible to determine which scan method among the zig-zag scan, the vertical scan, and the horizontal scan is to be used.

[0065] The entropy encoding unit (165) can perform entropy encoding based on the values ​​produced by the rearrangement unit (160). Entropy encoding can use various encoding methods such as, for example, Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC). In this regard, the entropy encoding unit (165) can encode residual value coefficient information of the encoding unit from the rearrangement unit (160) and the prediction units (120, 125). In addition, according to the present disclosure, it is possible to signal and transmit information indicating that motion information is derived and used on the decoder side and information on a technique used to derive motion information.

[0066] The inverse quantization unit (140) and the inverse transformation unit (145) inversely quantize the values ​​quantized in the quantization unit (135) and inversely transform the values ​​transformed in the transformation unit (130). The residual values ​​generated in the inverse quantization unit (140) and the inverse transformation unit (145) can be combined with the predicted prediction units predicted through the motion estimation unit, motion compensation unit, and intra prediction unit included in the prediction unit (120, 125) to generate a reconstructed block.

[0067] The filter unit (150) may include at least one of a deblocking filter, an offset correction unit, and an ALF (Adaptive Loop Filter). The deblocking filter may remove block distortion caused by boundaries between blocks in a restored picture. The offset correction unit may correct the offset from the original image on a pixel-by-pixel basis for the image on which deblocking has been performed. In order to perform offset correction for a specific picture, a method may be used in which the pixels included in the image are divided into a certain number of regions, the regions to be offset are determined, and the offset is applied to the regions, or the offset is applied by considering edge information of each pixel. The ALF (Adaptive Loop Filtering) may be performed based on a value obtained by comparing the filtered restored image with the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group is determined, and filtering may be performed differentially for each group.

[0068] The memory (155) can store a restored block or picture produced through the filter unit (150), and the stored restored block or picture can be provided to the prediction unit (120, 125) when performing inter prediction.

[0069] FIG. 2 is a block diagram showing an image decoding device according to the present disclosure.

[0070] Referring to FIG. 2, the image decoding device (200) may include an entropy decoding unit (210), a rearrangement unit (215), an inverse quantization unit (220), an inverse transformation unit (225), a prediction unit (230, 235), a filter unit (240), and a memory (245).

[0071] When a video bitstream is input to a video encoding device, the input bitstream can be decoded in the opposite procedure to that of the video encoding device.

[0072] The entropy decoding unit (210) can perform entropy decoding in a procedure opposite to that of the entropy encoding unit of the video encoder. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) can be applied in response to the method performed in the video encoder.

[0073] The entropy decoding unit (210) can decode information related to intra prediction and inter prediction performed in the encoder.

[0074] The reordering unit (215) can perform reordering based on the method by which the bitstream entropy-decoded by the entropy decoding unit (210) is reordered by the encoding unit. The coefficients expressed in the form of a one-dimensional vector can be reordered by restoring them back to coefficients in the form of a two-dimensional block.

[0075] The inverse quantization unit (220) can perform inverse quantization based on the quantization parameters provided by the encoder and the coefficient values ​​of the rearranged block.

[0076] The inverse transform unit (225) can perform inverse transform, i.e., inverse DCT, inverse DST, and inverse KLT, on the transforms performed by the transform unit, i.e., DCT, DST, and KLT, on the quantization result performed by the image encoder. The inverse transform can be performed based on the transmission unit determined by the image encoder. In the inverse transform unit (225) of the image decoder, a transform technique (e.g., DCT, DST, KLT) can be selectively performed according to a plurality of pieces of information, such as a prediction method, the size of the current block, and the prediction direction.

[0077] The prediction unit (230, 235) can generate a prediction block based on prediction block generation related information provided from the entropy decoding unit (210) and previously decoded block or picture information provided from the memory (245).

[0078] As described above, when performing intra prediction or intra prediction in the same manner as the operation in the image encoder, if the size of the prediction unit and the size of the transformation unit are the same, intra prediction for the prediction unit is performed based on the pixels on the left side of the prediction unit, the pixels on the upper left side, and the pixels on the upper side. However, when performing intra prediction, if the size of the prediction unit and the size of the transformation unit are different, intra prediction can be performed using reference pixels based on the transformation unit. In addition, intra prediction using NxN division only for the minimum coding unit can be used.

[0079] The prediction unit (230, 235) may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit may receive various information such as prediction unit information input from the entropy decoding unit (210), prediction mode information of an intra prediction method, and motion prediction-related information of an inter prediction method, and may distinguish a prediction unit from a current encoding unit and determine whether the prediction unit performs inter prediction or intra prediction. On the other hand, if the encoder (100) does not transmit motion prediction-related information for the inter prediction, but instead transmits information indicating that motion information is to be derived and used on the decoder side and information on a technique used to derive motion information, the prediction unit determination unit determines whether the inter prediction unit (230) performs prediction based on the information transmitted from the encoder (100).

[0080] The inter prediction unit (230) can perform inter prediction on the current prediction unit based on information included in at least one picture among the previous picture or the subsequent picture of the current picture including the current prediction unit, using information required for inter prediction of the current prediction unit provided by the image encoder. In order to perform inter prediction, it can be determined based on the encoding unit whether the motion prediction method of the prediction unit included in the corresponding encoding unit is one of Skip Mode, Merge Mode, AMVP Mode, Intra Block Copy Mode, and Affine Mode.

[0081] The intra prediction unit (235) can generate a prediction block based on pixel information within the current picture. If the prediction unit is a prediction unit that has performed intra prediction, intra prediction can be performed based on intra prediction mode information of the prediction unit provided by the image encoder.

[0082] The intra prediction unit (235) may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolation unit, and a DC filter. The AIS filter is a unit that performs filtering on the reference pixels of the current block and can determine whether to apply the filter based on the prediction mode of the current prediction unit and apply it. AIS filtering can be performed on the reference pixels of the current block using the prediction mode and AIS filter information of the prediction unit provided by the image encoder. If the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

[0083] The reference pixel interpolation unit can interpolate the reference pixel to generate a reference pixel of a pixel unit less than an integer value when the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on the pixel value interpolated from the reference pixel. When the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

[0084] The restored block or picture may be provided to a filter unit (240). The filter unit (240) may include a deblocking filter, an offset correction unit, and an ALF.

[0085] Information about whether a deblocking filter has been applied to a corresponding block or picture can be received from a video encoding device, and if a deblocking filter has been applied, information about whether a strong or weak filter has been applied. The deblocking filter of the video decoder can receive information related to the deblocking filter provided by the video encoder, and the video decoder can perform deblocking filtering on the corresponding block.

[0086] The offset correction unit can perform offset correction on the restored image based on the type of offset correction applied to the image during encoding and information on the offset value. ALF can be applied to the encoding unit based on information on whether ALF is applied and ALF coefficient information provided from the encoder. This ALF information can be provided by being included in a specific parameter set.

[0087] The memory (245) can store a restored picture or block so that it can be used as a reference picture or reference block, and can also provide the restored picture to an output unit.

[0088] FIG. 3 illustrates an intra prediction method according to the present disclosure.

[0089] Referring to FIG. 3, an intra merge list for the current block can be constructed (S300).

[0090] The intra merge list of the current block may include multiple candidates. Here, the candidates may include at least one of an intra prediction mode, a block vector, information for intra prediction, or information about a reference block.

[0091] Candidates in the intra-merge list of the current block can be derived based on a reference block. The reference block may be a previously restored block within the current picture to which the current block belongs, or a block within a previously restored reference picture.

[0092] A candidate in an intra merge list may include prediction information of a reference block. Here, the prediction information may include at least one of an intra prediction mode or a block vector. For example, the candidate may include at least one of a directional or non-directional intra prediction mode of the reference block. The non-directional intra prediction mode may include at least one of a planar mode, a DC mode, or a Matrix-based Intra Prediction (MIP) mode. The planar mode according to the present disclosure may include at least one of a non-directional planar mode or a directional planar mode, and the directional planar mode may include at least one of a horizontal planar mode or a vertical planar mode. Here, the non-directional planar mode may refer to a planar mode that refers to top and left peripheral samples. In contrast, the horizontal planar mode may refer to a planar mode that refers to left peripheral samples, and the vertical planar mode may refer to a planar mode that refers to top peripheral samples.

[0093] When the reference block uses a method for deriving an intra prediction mode, the candidate may include whether the decoder side uses a method for deriving an intra prediction mode or at least one of the intra prediction modes already derived from the reference block. For example, the method for deriving the intra prediction mode may mean a method for deriving an intra prediction mode based on at least one of decoder side intra prediction derivation (DIMD), template based intra mode derivation (TIMD), occurrence-based intra coding (OBIC), template-based multiple reference lines (TMRL), or most probable mode (MPM).

[0094] When a reference block generates a prediction block based on an IBC (Intra Block Copy) or IntraTMP (Intra template matching prediction) prediction technique, the candidate may include at least one of information about the prediction technique used by the reference block or a block vector of the reference block.

[0095] A candidate in an intra merge list according to the present disclosure may further include information used by a reference block when performing intra prediction.

[0096] For example, if a reference block generates a prediction block based on multiple reference lines, the candidate may include information about the reference lines of the reference block. The information about the reference lines may include a reference line index that specifies the reference lines of the reference block.

[0097] When a reference block generates a prediction block based on an intra sub-block prediction (ISP) mode, the candidate may include information about the ISP mode of the reference block. Here, the information about the ISP mode may include at least one of information about whether the ISP mode is applied, information about the splitting direction, or information about the number of split sub-blocks.

[0098] When a reference block performs geometric partitioning, the candidate may include information regarding the geometric partitioning of the reference block. The information regarding the geometric partitioning may include information regarding at least one of a partitioning angle or a partitioning distance.

[0099] If the reference block uses MIP mode, the candidate may include at least one of the matrix index or transpose flag of the reference block.

[0100] When a reference block generates a prediction block based on a weighted sum of multiple prediction blocks, the candidate may include information regarding weights of the prediction blocks used in the weighted sum. Here, the weighted sum may be performed between prediction blocks generated through an intra prediction mode, and may also be performed between prediction blocks generated through a block vector. Alternatively, the weighted sum may be performed between a prediction block generated through an intra prediction mode and a prediction block generated through a block vector.

[0101] When a reference block generates a prediction block based on a block vector, the candidate may include information regarding the difference between the template region at the location referenced by the block vector of the reference block and the template region of the current block. Here, the information regarding the difference between the template regions may refer to a template cost, and the template cost may be calculated through the Sum of Absolute Differences (SAD) or Mean Squared Error (MSE) between the template regions.

[0102] Alternatively, if the reference block already has multiple template costs, information about the difference between the template regions included in the candidate may be replaced with a template cost based on the difference between the template region of the current block and the template region of the reference block.

[0103] Alternatively, information regarding the difference between the template regions can be updated through a weighted sum between the template cost based on the reference block and the template cost based on the current block. The template cost based on the reference block may refer to a template cost based on the difference between the template region at a location referenced by the block vector of the reference block and the template region of the reference block. The template cost based on the current block may refer to a template cost based on the difference between the template region at a location referenced by the block vector of the reference block and the template region of the current block. In addition, multiple template costs of the reference block may be included as candidates.

[0104] If the reference block generates a prediction block through at least one of a linear or non-linear combination technique, the candidate may include information regarding the combination technique of the reference block. Here, the combination technique may include at least one of a linear filter model, a convolution filter model, or local illumination compensation.

[0105] When a reference block uses a prediction method that implicitly derives an intra prediction mode based on a predetermined filter, the candidate may include at least one of information about a gradient derived through the filter, an intra prediction mode corresponding to the gradient, an amplitude value, or a weight derived through the amplitude. Here, the filter may be for deriving a change or gradient of sample values ​​in a pre-restored surrounding area. A method for deriving an intra prediction mode based on a filter may include Decoder-side Intra Mode Derivation (DIMD), etc. Here, the filter may mean a filter that derives a gradient based on a difference in a luma component value. Meanwhile, the filter may include a Sobel filter, and the Sobel filter may also be called a Sobel operator.

[0106] When a reference block uses a prediction method that implicitly derives an intra prediction mode based on a template cost, the candidate may include at least one of information about the template cost of the reference block or a weight derived from the template cost. Methods for deriving an intra prediction mode based on a template cost may include Template-based Intra Mode Derivation (TIMD), Template Matching Reference List (TMRL), or Intra Template Matching Prediction (IntraTMP). Here, the template cost may refer to a difference in a template area between a reference block and a block referenced by the reference block. Alternatively, the template cost may refer to a difference in a template area between a reference block and a current block. Alternatively, the template cost may refer to a difference in a template area between a current block and a block referenced by the reference block. The template cost may be calculated through Sum of Absolute Differences (SAD) or Mean Squared Error (MSE) between template areas.

[0107] When a reference block uses a method for specifying an intra prediction mode based on the intra prediction mode distribution of surrounding blocks, the candidate may include information about at least one of an intra prediction mode distribution (Histogram of Occurrence) of the reference block or a Most Probable Mode (MPM). The method for specifying an intra prediction mode based on the intra prediction mode distribution may include a method for deriving an intra prediction mode based on at least one of Occurrence-based Intra Coding (OBIC) or MPM.

[0108] A candidate within the intra-merge list according to the present disclosure may further include information about the reference block. For example, the candidate may include information regarding the size of the reference block. Here, the size information may include information regarding at least one of the width, height, or number of pixels belonging to the reference block (i.e., the product of the width and height of the reference block).

[0109] The above candidate may include information regarding the transformation method used to restore the reference block. The transformation method may include a Discrete Cosine Transform (DCT) or a Discrete Sine Transform (DST).

[0110] The above candidate may include information about quantization coefficients of a reference block.

[0111] The above candidate may include information regarding in-loop filter parameters of the reference block. The in-loop filter parameters may include a Deblocking Filter (DBF), a Sample Adaptive Offset (SAO), or an Adaptive Loop Filter (ALF).

[0112] A list of reference blocks that can be used for intra or inter prediction can be added to the intra merge list. The list that can be used for intra prediction can include at least one of a candidate list for IBC or an MPM list. Additionally, the list that can be used for inter prediction can include at least one of a candidate list for Advanced Motion Vector Prediction (AMVP) mode or a candidate list for merge mode.

[0113] The intra merge list according to the present disclosure may be a single, integrated intra merge list. Alternatively, the intra merge list according to the present disclosure may be a plurality of intra merge lists separated by intra prediction mode determination methods.

[0114] If the intra merge list of the current block is a single, unified intra merge list, the number of intra prediction modes that can be included as candidates may be limited to N or less, where N may be an integer greater than or equal to 1. Different numbers of intra prediction modes may be included as candidates depending on the intra prediction mode determination method. For example, the number of intra prediction modes based on DIMD may be 2 or less, and the number of intra prediction modes based on TIMD may be 4 or less.

[0115] Referring to FIG. 3, a prediction block of the current block can be generated based on a candidate in the intra merge list for the current block (S310).

[0116] The predicted block of the current block can be generated based on any one of multiple candidates belonging to the intra merge list.

[0117] Alternatively, prediction blocks may be generated based on at least two of a plurality of candidates belonging to the intra merge list, and the prediction block of the current block may be generated based on a weighted sum between the generated prediction blocks.

[0118] For example, a template cost can be derived for each candidate in an intra merge list. Here, the template cost for each candidate can be derived based on the candidate's intra prediction mode (or block vector) and the template region of the current block. A prediction block for the current block can be generated based on M candidates in ascending order of the derived template costs. Here, M can be an integer greater than or equal to 1.

[0119] Alternatively, K prediction blocks can be generated based on candidates corresponding to the top K candidate indices in ascending order of candidate indices within the intra merge list. A prediction block of the current block can be generated based on a weighted sum of the generated prediction blocks. Here, K can be an integer greater than or equal to 1.

[0120] Alternatively, P prediction blocks can be generated based on P candidates corresponding to odd or even candidate indices in the intra merge list. A prediction block of the current block can be generated based on a weighted sum of the generated prediction blocks. Here, P can be an integer greater than or equal to 1. In this case, the intra merge list can be reordered based on the template cost of each candidate described above.

[0121] When the intra merge list according to the present disclosure is a plurality of intra merge lists separated by the intra prediction mode determination method of the reference block, L prediction blocks can be generated based on candidates corresponding to the top L candidate indexes in ascending order of candidate indexes in each intra merge list. A prediction block of the current block can be generated based on a weighted sum of the generated prediction blocks. Here, L can be an integer greater than or equal to 0. Each intra merge list can have a different value. For example, in the case of a DIMD-based intra merge list, L can be 0. On the other hand, in the case of a TIMD-based intra merge list, L can be 2. In this case, the plurality of intra merge lists can be reordered based on the template cost of each candidate described above.

[0122] If at least one candidate in the intra merge list is an intra prediction method that generates a prediction block based on a weighted sum between multiple prediction blocks generated based on intra prediction modes or block vectors, the prediction block of the current block can be generated based on a weighted sum between prediction blocks generated based on the top G intra prediction modes or block vectors having high weights. Here, G may be an integer greater than or equal to 0, and may have different values ​​for each prediction mode of the reference block.

[0123] The weights for the above weighted sum may be explicitly signaled or implicitly derived.

[0124] For example, the weights used in the weighted sum can be derived based on information regarding the weights for each intra prediction mode or block vector of the reference block. In this case, if information regarding the weights of the reference block exists in the candidate, the weight information can be used as is, or it can be used after being adjusted according to the number of prediction blocks to be used in the weighted sum.

[0125] Alternatively, the template cost can be calculated by applying a higher weight to a prediction block with a lower template cost by calculating the template cost for the intra prediction mode or block vector used in the weighted sum. Here, the template cost can be calculated based on the template region of the current block.

[0126] The encoder can perform prediction based on candidates in an intra merge list, and determine an optimal candidate index based on rate-distortion optimization (RDO) based on the prediction. The encoder can signal the determined candidate index to a decoder. In addition, if the intra merge list is a plurality of intra merge lists configured according to an intra prediction mode determination method of a reference block, the encoder can further include a list index determination step for selecting one intra merge list from among the plurality of intra merge lists. In this case, the encoder can additionally signal the determined list index to the decoder.

[0127] For example, the decoder may implicitly derive at least one of the candidate index or the list index based on the result of constructing the intra-merge list. For example, if a unified single merge list is constructed, the encoder may omit the syntax signaling of at least one of the intra-merge list usage flag, the list index, and the candidate index.

[0128] The encoder can encode candidate indices for the current block.

[0129] When multiple intra merge lists are configured for each method of determining the intra prediction mode of the reference block, the encoder may signal a flag indicating whether to use the intra merge list after signaling a list index for selecting one intra merge list from among the multiple intra merge lists. Alternatively, the list index may be signaled after signaling the flag indicating whether to use the intra merge list.

[0130] Alternatively, a flag indicating whether to use an intra-merge list may be signaled after signaling at least one of the list index or candidate index. Furthermore, if the current block generates a final prediction block based on a weighted sum of prediction blocks generated based on candidates within the intra-merge list, at least one piece of information regarding the weights used in the weighted sum may be additionally signaled.

[0131] The various embodiments of the present disclosure are not intended to list all possible combinations but rather to illustrate representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combination of two or more.

[0132] Additionally, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, the embodiments may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general processors, controllers, microcontrollers, microprocessors, etc.

[0133] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be executed on a device or a computer, and a non-transitory computer-readable medium having such software or instructions stored thereon and executable on the device or computer.

[0134] The present disclosure can be industrially utilized in the fields of methods, devices, and recording media for video encoding / decoding.

Claims

1. A step for constructing an intra-merge list for the current block; and A step of generating a prediction block for the current block based on at least one of a plurality of candidates belonging to the intra merge list, Candidates belonging to the above intra merge list are derived based on the reference block, A method for decoding an image, wherein the above reference block belongs to at least one of the current picture or the reference picture.

2. In paragraph 1, A method for decoding an image, wherein the candidate comprises at least one intra prediction mode having directionality or non-directionality of the reference block.

3. In paragraph 1, A method for decoding an image, wherein, when the above reference block uses a method for deriving an intra prediction mode, the candidate includes information on whether the decoder side uses a method for deriving an intra prediction mode and an intra prediction mode already derived from the above reference block.

4. In paragraph 1, A method for decoding an image, wherein, if the reference block has a block vector, the candidate includes information about the intra prediction method used by the reference block and the block vector of the reference block.

5. In paragraph 1, A method for decoding an image, wherein when the reference block generates a final prediction block based on a weighted sum of prediction blocks generated in an intra prediction mode or prediction blocks generated with a block vector, the candidate includes information about weights applied to prediction blocks used in the weighted sum.

6. In paragraph 1, A method for decoding an image, wherein when the above reference block generates a prediction block based on a block vector, the candidate includes information about the difference between the template area of ​​the location referenced by the block vector of the reference block and the template area of ​​the current block.

7. In paragraph 1, When the above reference block uses a prediction method that implicitly derives an intra prediction mode based on a gradient filter, the candidate includes at least one of information about a value of amplitude derived through the gradient filter or information about a weight derived through the value of amplitude, The above gradient filter is an image decoding method that means a filter that induces a gradient based on the difference in luma component values.

8. In paragraph 1, If the above reference block uses a prediction method that implicitly derives an intra prediction mode based on a template cost, the candidate includes at least one of information about the template cost or a weight derived through the template cost, A method for decoding an image, wherein the template cost means at least one of a difference between a template area between the reference block and a block referenced by the reference block, or between the reference block and the current block, or between a block referenced by the reference block and the current block.

9. In paragraph 1, The above candidate includes information about the above reference block, A method for decoding an image, wherein the information about the reference block includes at least one of the size of the reference block, the transformation method used for restoration, the transformation quantization coefficients, the filter parameters within the loop, the heterogeneous list usable in intra prediction, or the heterogeneous list usable in inter-screen prediction.

10. In paragraph 1, A screen decoding method, wherein a plurality of intra merge lists separated by the intra prediction mode determination method are generated based on the intra prediction mode determination method of the above reference block.

11. In paragraph 1, The prediction block of the current block is generated based on a weighted sum between prediction blocks generated based on candidates corresponding to the top K list indices in the intra merge list, An image decoding method, wherein the above K is a natural number.

12. Step of constructing an intra-merge list for the current block; and A step of generating a prediction block for the current block based on at least one of a plurality of candidates belonging to the intra merge list, Candidates belonging to the above intra merge list are derived based on the reference block, A method for encoding an image, wherein the above reference block belongs to at least one of the current picture or the reference picture.

13. A computer-readable storage medium for storing a bitstream generated by the image encoding method according to Article 12.

14. Step of constructing an intra merge list for the current block; and A step of generating a bitstream by performing a prediction on the current block based on at least one of a plurality of candidates belonging to the intra merge list, Candidates belonging to the above intra merge list are derived based on the reference block, A bitstream transmission method, wherein the above reference block belongs to at least one of the current picture or the reference picture.

Images